The present invention relates to improvements in or relating to horizontal endless belt vacuum filters.
Filters of this type are already known, which essentially comprise an endless conveyor belt made of rubber, extending horizontally between two drums and whose cross section is in the form of a trough when longitudinal and lateral beads are present. The bottom of this belt presents outwardly open, transverse grooves allowing the liquid resulting from filtration to flow towards orifices pierced in the central part of the belt. On this conveyor belt is disposed a filtering medium constituted, for example, by a cloth on which the matter to be filtered is disposed. Beneath the upper side of the conveyor belt is located a vacuum box extending longitudinally and whose upper part, which is open, lies below the central orifices of the conveyor belt. This vacuum box which is connected to a source of vacuum, collects, by suction, the filtrate coming from the mass to be filtered.
In such belt filters, the vacuum box which constitutes an important part of the filter, is subjected to frequent operations of maintenance and/or cleaning and to this end various devices for manoeuvring the vacuum box have already been provided for facilitating these operations. The known devices for manoeuvring the vacuum box comprise various mechanisms such as counterweights, cable or chain winches, pneumatic, electrical or hydraulic jacks, racks, screws, jacks, articulated parallelograms, etc. Now, these devices are not very practical to use and they present numerous drawbacks. In fact, the counterweights are cumbersome especially when water is used as weighty element. The winches must be maintained clean and when the vacuum box is long, it is necessary to manoeuvre several winches in synchronism, otherwise the vacuum box would be twisted. As for the jacks, they require a particular energy source, good protection and continuous maintenance. Regarding the other mechanical devices mentioned, they are expensive and require good maintenance. In addition, none of the known devices for manoeuvring the vacuum box makes it possible to distribute the suction over the whole length of the vacuum box.
Furthermore, another drawback presented by most of the heretofore known endless belt filters is that their vacuum box is made in one piece, in sheet metal, so as to present substantially U-shaped cross section, with narrowed upper opening which is bordered by two lateral coplanar flanges extending outwardly. A vacuum box made in this way in one piece is difficult to manufacture with sufficient precision and it is not easy to clean and to position and/or to displace intermediate partitions. Furthermore, the two upper horizontal flanges bordering the vacuum box bear longitudinal strips for slide of the conveyor belt, which strips tend to be permanently drawn towards the upper opening of the vacuum box, due to the depression created in this box.
Belt filters also provided with a mechanism ensuring the correct tensioning of the filtering medium, this mechanism generally employing a weighty roller acting by its weight on one side of the filtering medium. However, the associated devices for lifting the weighty roller in order to slacken the filtering medium are generally relatively complicated and not easy to emply.